This invention relates to apparatus for detecting magnetic phenomena and is more particularly concerned with an improved magnetic locator.
Devices for locating magnetic objects and/or for detecting or measuring magnetic fields are well known. Such devices may comprise a plurality of magnetic sensor units, including appropriate windings or coils, which are spaced apart and mounted within a non-magnetic tubular housing. See, for example, U.S Pat. No. 3,894,283, granted July 8, 1975, and assigned to the same assignee as the present invention, incorporated herein by reference. The external configuration of the apparatus described in that patent resembles a broomstick with a can at one end thereof. The "broomstick" is actually an elongated tubular housing, and the "can" is a tubular housing of larger diameter fixed to one end of the broomstick. The exemplary structure described in the patent employs earphones connected to electronics in the "can" to produce audible signals indicative of detected magnetic objects. It is well known in the prior art of metal detectors to employ a loudspeaker to produce audio signals, but prior metal detectors with loudspeakers have left much to be desired.
When earphones are employed in a magnetic locator, it is a simple matter to provide a phone jack at a convenient location on a fixed portion of the can which houses the electronics. However, providing a loudspeaker in a magnetic locator is not a simple matter. First of all, to protect the loudspeaker, it should be mounted in a housing, preferably, for simplicity, the same housing containing the electronics of the locator. Openings must then be provided in the housing for the passage of sound from the loudspeaker to the exterior of the housing, but rain entering the housing through the openings can damage the loudspeaker and other components in the housing. Access to the interior of the housing must be provided for the replacement of batteries or other maintenance, and the mounting of the loudspeaker should not impede such access. Also, since conventional loudspeakers usually have magnetic parts, the magnetic effect of the loudspeaker must be balanced out or compensated so that the locator will operate properly, and compensation should not change once it is properly set by the manufacturer of the locator. Furthermore, since magnetic locators are frequently subjected to rough use, the loudspeaker mounting arrangement should be capable of handling shock forces without damage to the loudspeaker.